Higher density multi-component and serial packages

ABSTRACT

A high density multi-component package is provided. The package has at least two electronic components wherein each electronic component comprises a first external termination and a second external termination. At least one first adhesive is between adjacent first external terminations of adjacent electronic components. At least one second adhesive is between the adjacent electronic component and at least two adjacent electronic components are connected serially. The first adhesive and second adhesive are independently selected from a high temperature conductive adhesive and a high temperature insulating adhesive.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of pending U.S.patent application Ser. No. 15/852,799 filed Dec. 22, 2017 which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention is related to a high-density package of electroniccomponents, and a method of making the package, wherein increasedfunctionality can be achieved in a limited footprint. More specifically,the present invention is specific to a high-density package comprisingcombinations of high temperature conductive adhesive and hightemperature insulating adhesive between adjacent electronic componentswhich allow for serial connectivity of a variety of electroniccomponents.

BACKGROUND

There is an on-going need in electronics to provide increasedfunctionality in increasingly smaller devices. This desire, referred toas miniaturization, has dominated research efforts associated withcomponents, mounting techniques and the like. While most of the efforthas been focused on decreasing the footprint of electronic components ona circuit board more recent efforts have focused on stacking componentsthereby occupying the space above and below the board instead ofoccupying surface area of the board.

Stacked multi-layer ceramic capacitors (MLCC) are described in commonlyassigned U.S. Pat. No. 9,472,342, to McConnell et al., which isincorporated herein by reference, wherein leadless multi-layer ceramiccapacitors are formed in stacks where two or more MLCC's are bondedtogether by their terminations using transient liquid phase sintering(TLPS) adhesives. The resulting stack can be surface mounted bytechniques known in the art, such as soldering, since the TLPS does notreflow at the soldering temperature.

While advantageous, the leadless stacks provide capacitors in electricalparallel only and therefore the applications are somewhat limited. Thereare many applications requiring electronic components seriallyconnected. Serially connected components can be achieved by bonding theterminals of the respective components end-to-end, rather than in astack, however this increases the space required for mounting which iscontrary to the overwhelming desire for miniaturization.

There is an ongoing necessity for a package comprising multiplecomponents, which can be serially connected, while minimizing thefootprint of the package on the circuit board. Provided herein is animproved package for multiple components, preferably including at leastone MLCC, wherein at least some of the electronic components in thepackage are serially connected.

SUMMARY OF THE INVENTION

The present invention is related to high density multi-componentpackages.

More specifically, the present invention is related to high densitymulti-component packages which allow for serial or parallel connectivityof different components in the package.

A particular feature of the invention is the ability to mount a highdensity package on a circuit board either vertically or horizontally.

These and other embodiments, as will be realized, are provided in a highdensity multi-component package. The package has at least two electroniccomponents wherein each electronic component comprises a first externaltermination and a second external termination. At least one firstadhesive is between adjacent first external terminations of adjacentelectronic components. At least one second adhesive is between theadjacent electronic component and at least two adjacent electroniccomponents are connected serially. The first adhesive and secondadhesive are independently selected from a high temperature conductiveadhesive and a high temperature insulating adhesive

Yet another embodiment is provided in an electronic circuit. Theelectronic circuit has a high density multi-component package whereinthe package comprises at least two electronic components wherein eachelectronic component comprises a first external termination and a secondexternal termination, at least one first adhesive between adjacent firstexternal terminations, at least one second adhesive between adjacentelectronic components and wherein at least two adjacent electroniccomponents are connected serially. The first adhesive and secondadhesive are independently selected from a high temperature conductiveadhesive and a high temperature insulating adhesive. The electroniccircuit also comprises a circuit board comprising traces wherein atleast one trace is an active trace and at least one trace of said tracesis a mechanical trace. At least one first external termination of afirst electronic component is in electrical contact with one activetrace. At least one second external termination of a second electroniccomponent is in electrical contact with a mechanical trace.

Yet another embodiment is provided in a method for forming a highdensity multi-component package. The method includes:

providing at least two electronic components wherein each electroniccomponent comprises a first external termination and a second externaltermination;

forming a stack of adjacent electronic components;

attaching adjacent first external terminations with a first adhesivethere between;

attaching adjacent electronic components with a second adhesive therebetween;

wherein the first adhesive and second adhesive are independentlyselected from the group consisting of a high temperature conductiveadhesive and a high temperature insulating adhesive; and

wherein the adjacent electronic components are connected serially.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic side view representation of an embodiment of theinvention.

FIG. 2 is a schematic side view representation of an embodiment of theinvention.

FIG. 3 is a schematic cross-sectional side view representation of anembodiment on the invention.

FIG. 4 is a schematic cross-sectional side view representation of anembodiment on the invention.

FIG. 5 is a schematic top view representation of an embodiment of theinvention.

FIG. 6 is a schematic top view representation of an embodiment of theinvention.

FIG. 7 is an electrical schematic representation of an embodiment of theinvention.

FIG. 8 is an electrical schematic representation of an embodiment of theinvention.

FIG. 9 is a schematic top view representation of an embodiment of theinvention.

FIG. 10 is a schematic side view representation of an embodiment of theinvention.

FIG. 11 is an electrical schematic representation of an embodiment ofthe invention.

FIG. 12 is an electrical schematic representation of an embodiment ofthe invention.

FIG. 13 is schematic side view representation of an embodiment of theinvention.

FIG. 14 is schematic side view representation of an embodiment of theinvention.

FIG. 15 is an electrical schematic representation of an embodiment ofthe invention.

FIG. 16 is an electrical schematic representation of an embodiment ofthe invention.

FIG. 17 is an electrical schematic representation of an embodiment ofthe invention.

FIG. 18 is a schematic side view representation of an embodiment on theinvention.

FIG. 19 is a schematic side view representation of an embodiment on theinvention.

FIG. 20 is a schematic cross-sectional side view representation of anembodiment on the invention.

FIG. 21 is a schematic cross-sectional side view representation of anembodiment on the invention.

FIG. 22 is an electrical schematic representation of an embodiment ofthe invention.

FIG. 23 schematic cross-sectional top view representation of anembodiment on the invention.

FIGS. 24 and 25 are electrical schematic representations of embodimentsof the invention.

FIG. 26 is an electrical schematic representation of an embodiment ofthe invention.

FIG. 27 schematic cross-sectional top view representation of anembodiment on the invention.

FIG. 28 is a schematic cross-sectional side view representation of anembodiment on the invention.

FIG. 29 is a schematic cross-sectional side view representation of anembodiment on the invention.

DESCRIPTION

The present invention is related to a high density multi-componentpackage of electronic components wherein at least some of the electroniccomponents are serially connected and the package minimizes surface arearequired on the circuit board. More specifically, the present inventionis related to a stack of electronic components comprising a combinationof high temperature conductive adhesives (HTCA) and high temperatureinsulating adhesives (HTIA) between adjacent external terminations ofadjacent electronic components or between adjacent electroniccomponents.

The high density multi-component package of the present inventioncomprises a combination of HTCA and HTIA between adjacent electroniccomponents thereby providing for a serial configuration. Previous artrequires indirect connections via addition of interposers and HTCAmaterials between components or linking of components via connectionsvia traces in the control board strata. In the present invention theHTCA provides for an electrical connection between terminals of adjacentcomponents within the stack of electronic components. The HTIA providesa mechanical bond and electrical insulation between adjacent components.The combination of HTCA and HTIA allows components to be arranged in ahigher density package with serial and parallel connectivity. Thiscompaction can be beneficial in either the vertical or horizontalmounting configuration. In one embodiment, the package of electroniccomponents can be surface mounted with the end terminals of theoutermost components electrically connected to the circuit. The highdensity multi-component package can be used to form high densitypackages containing mixed electronic components and provides theflexibility to connect the electronic component in electrical series aswell as in electrical parallel thereby enabling high density packages ofmultifunctional components with a variety of electronic configurations.The HTCA and HTIA can be bonded in the same process or separately.Furthermore, the components can be formed into a bonded stack and thestack mounted to a circuit board or the circuit board mounting and stackformation can occur in concert.

The invention will be described with reference to the figures forming anintegral, non-limiting, component of the disclosure. Throughout thevarious figures similar elements will be numbered accordingly.

An embodiment of the invention will be described with reference to FIG.1 wherein a high density multi-component package, 30, is illustrated inschematic side view. In FIG. 1, four electronic components areillustrated for the purposes of discussion without limit thereto. Eachelectronic component is arbitrarily numbered for the purposes ofillustration and discussion only. In FIG. 1, HTCA's, 10, and HTIA's, 11,are between adjacent external terminations of adjacent electroniccomponents. Each electronic component has one external termination, 32,in either electrical contact with and adjacent external terminationthrough a HTCA, 10, or physically attached with a insulating bondthrough a HTIA, 11, which is preferably between adjacent externalterminations. In FIG. 1 an electronic path is formed beginningarbitrarily at external termination, 32 ¹, of electronic component 1,and ending with external termination, 32 ⁸, of electronic component 4.The four electronic components are therefore all serially connected.While four electronic components are a sufficient number to illustratethe invention it is to be understood that the invention can be extendedfrom two components to any number of electronic components and a largevariety of variations as will be realized. It is preferable that thenumber of components is at least two to no more than 100.

An embodiment of the invention will be described with reference to FIG.2 wherein a high density multi-component package vertically mounted to asubstrate, 36, is illustrated in schematic side view. Active circuittraces, 38, on the substrate, 36, are in functional electronicconnection with external terminations, 32 ¹ and 32 ⁸. Externaltermination, 32 ¹, is directly attached to active circuit trace 38 ¹ byan interconnect, 42, which may be the same as the HTCA forming theinterconnect between adjacent external terminations or it may bedifferent. A connector, 44, is in electrical contact with externaltermination 32 ⁸ and active trace 38 ² wherein the active traces, 38,are integral to the electronic circuit of a device, 30. The connectormay be an electrical connection and otherwise provide no furtherfunction or the connector may be a functional connection such as anelectrical component. Particularly preferred connectors include aresistor, a fuse, an inductor or a flexible circuit. A mechanical trace,40, provides mechanical stability and is directly attached to externaltermination 32 ² by an interconnect, 42.

An embodiment of the invention will be described with reference to FIGS.3 and 4 wherein a flex circuit is utilized as the connector. Withreference to FIG. 3 a flex circuit connector, 144, shown incross-sectional schematic view, comprises a flexible substrate, 160. Anoptional but preferred mechanical pad, 20, provides for mechanicalattachment to an external termination, 32 ⁶ of FIG. 4, or between thebody of the electronic components, for mechanical robustness. A pair ofconducting pads, 18, are in electrical connection with vias, 14, whichare in electrical contact with a trace, 146. A conducting pad is inelectrical contact with an external termination, 32 ⁵, and a conductingpad is in electrical contact with a circuit trace, 38 ².

An embodiment of the invention will be described with reference to FIG.5 wherein a high density multi-component package horizontally mounted toa circuit board, 36, is illustrated in schematic top view. In FIG. 5,each external termination, 32, is attached to a trace of the circuitboard with external terminations 32 ¹ and 32 ⁸ attached to active traces38 ¹ and 38 ², respectively, which are in electrical contact with thecircuit traces, 46. The remaining external terminations are attached tomechanical traces, 40, preferably through a solder pad, 43, by aninterconnect which is not shown. In FIG. 5 the electronic components areall serially connected. In FIG. 5 the HTIA is optional as the electroniccomponents are mechanically secured to the circuit board. The HTIA isstill preferable as it provides mechanical stability and thus allows forthe manufacture of a stack of electronic components prior to andindependent of the board mounting process. This also facilitates parttesting prior to board assembly.

An embodiment of the invention will be described with reference to FIG.6 wherein a high density multi-component package is illustrated inschematic top view mounted to a substrate, 36. In FIG. 6 electroniccomponents 1 and 4 are mounted as illustrated and described relative toFIG. 5. Electronic components 2 and 3 have a HTCA, 10, directly therebetween and therefore the electronic components 2 and 3 are inelectrical parallel. A generic electrical schematic diagram isillustrated in FIG. 7 wherein electronic components 2 and 3 are inelectrical parallel between serially connected electronic components 1and 4. An electrical schematic diagram is provided in FIG. 8 whereinelectrical component 1 is an inductor, electrical components 2 and 3 areMLCC's and electrical component 4 is a fuse thereby providing a fusedinductor capacitor high density component.

An embodiment of the invention will be described with reference to FIGS.9 and 10 wherein a portion of an electronic circuit of a device isillustrated in top schematic view in FIG. 9 and side schematic view inFIG. 10. For the purposes of discussion, a series of pads, 58, arenumbered sequentially. Traces, 54, connecting adjacent pads aredesignated by the pads being electrically connected. Trace 54 ²³, forexample, provides electrical conductivity between pads 58 ² and 58 ³.HTIA's, 11, are between adjacent electronic components wherein pads 58 ¹and 58 ⁸ provide connectivity to the circuit by traces, 56. A secondaryelectrical component, 5, electrically mounted in parallel withelectrical components 2 and 3 at the external termination provides acombination of serial and parallel electrical connections and component5 does not increase the surface area of the circuit board, 36, occupiedby the package, 111. A secondary electrical component is an electricalcomponent which is peripheral to the stack but electrically connectedthereto thus adding to the circuits capabilities without increasing itsfootprint. While demonstrated with five electrical components the numberand arrangement of electrical components is not limited herein.

A representative circuit diagram for the package illustrated in FIGS. 9and 10 is provided in FIG. 11 wherein electronic components 1, 2, 3 and4 are electrically serially connected and component 5 is electricallyparallel to components 2 and 3. An exemplary embodiment is illustratedin FIG. 12 wherein electronic component 1 is an inductor, electroniccomponents 2 and 3 are MLCC's, electronic component 5 is a resistor andelectronic component 4 is a fuse.

An embodiment of the invention will be described with reference to FIG.13 wherein a high density multi-component package mounted to asubstrate, 36, is illustrated in partial cross-sectional schematic view.In FIG. 13, the electronic components are in parallel adjacent stackswith a secondary electronic component, P, spanning across electroniccomponents N and M. In one embodiment, electronic component P could bean interposer or a flexible circuit with two active pads and a tracethere between for electrical connectivity between the active pads. Asillustrated, without limit thereto, pads, 62, are active pads inelectrical communication with circuit traces, not shown, and pads, 60,are mechanical pads which are not otherwise electrically connected tothe circuit. An over-molding, 64, may be included to prevent surfacearcing, to create a barrier to moisture penetration or to facilitatemechanical placement.

In a further embodiment of the invention by increasing the number ofactive connections to the circuit board it is possible to achieve anelectrical filter within a high density component package. Pi, T, and LCfilters are widely used in either feed through or surface mountconfigurations but there is a desire to continue to miniaturize thesepackages and provide a high-density surface mountable solution. Anexample of a Pi-filter package is shown in FIG. 14 wherein electroniccomponent 2 is an inductor and electronic components 1 and 3 are MLCC's.The input and output of the inductor is connected through an MLCC toground traces, 51, thereby providing a Pi filter with an electricalschematic diagram illustrated in FIG. 15. Only the active circuit tracesare shown in FIG. 14 and other non-active pads may be added for amechanical bond for increased mechanical stability. An electronicschematic diagram for an “LC” filter is illustrated in FIG. 16 and a “T”filter is illustrated in FIG. 17.

In the case where the component to be attached has a face-downtermination an active interposer with a reorientation via can be used asshown in FIG. 18 wherein a conducting pad, 18, is electrically connectedby a via, 14, to a conducting pad, 72. When used as depicted in FIG. 19one of the faced down terminals is connected to the circuit and theother to one terminal of the next component, 76, by connection to there-orientation via to form a serial connection. Each pad, 74,independently represent either mechanical pads or conducting pads asnecessary thereby allowing for flexibility in the design of theelectronic components and the functionality of the high densitymulti-component package.

An embodiment of the invention will be described with reference to FIG.20. In FIG. 20 a multiplicity of components, 1-8, are illustrated withadjacent components in one plane, 1 and 2 or 3 and 4 or 5 and 6 or 7 and8 for example, are serially connected through common electricalattachment by HTCA, 10. Adjacent components, such as 1 and 4, are inmechanical contact with HTIA, 11, there between. By providing multiplepads and combinations of HTCA and HTIA multiple arrangements ofcomponents can be provided in a limited space.

An embodiment of the invention will be described with reference to FIG.21. In FIG. 21, a combination of HTCA and HTIA provides the flexibilityto form serial and parallel electrical connections. Inter-stack HTCA,10, provides electrical conductivity between adjacent stacks, S₁ and S₂of components wherein, for the purposes of illustration, stack S₁comprises components 1, 2 and 3 and stack S₂ comprises components 4, 5and 6. For the purposes of illustration adjacent components 3 and 6 andadjacent components 2 and 5 provide a package with two groups ofcomponents 2-5 and 3-6 in electrical series with each set in electricalseries with component 1 and 4 as represented schematically in FIG. 22.In FIG. 21 the package is in electrical contact with active circuittraces, 38, on a circuit board, 36, with mechanical circuit traces, 40,provided for mechanical support. Alternatively, a mechanical circuittrace, 40 ¹ for example, may be an active circuit thereby allowing forthe use of a portion of the stack, only component 1 for example, withthe functionality of component 1, in this illustration, to be isolatedbetween traces 38 ¹ and 40 ¹. This allows for testing of individualcomponents within the package.

An embodiment of the invention will be described with reference to FIG.23 wherein a package is provided which allows multi-terminal componentsto be connected to the circuit through the use of HTCA and HTIA. In FIG.23 three components are illustrated, without limit thereto, with HTCAbetween adjacent components and with each external termination of eachcomponent in electrical contact with a circuit trace. Depending on thedesired functionality of the package some circuit traces, 151, can beactive and some can be mechanical. By way of example, traces 151 ^(A),151 ^(C) and 151 ^(B) can be active to provide the schematic of FIG. 24which could provide the T-filter of FIG. 17 when components 1 and 3 areinductors and component 2 is a capacitor. Alternatively, traces 151A,151B and 151E could be utilized to provide the schematic of FIG. 25which could provide the LC, or L filter of FIG. 17 when component 1 isan inductor and component 2 is a capacitor. By the use of alternatearrangements of HTCA and HTIA circuit traces 151A, 151B, 151C and 151Fcould be utilized to provide the schematic of FIG. 26 which couldprovide the Pi filter of FIG. 15 if components 1 and 3 are capacitorsand component 2 is an inductor. A single package can provide multiplefunctions. It would be understood that the number of components can bequite large and therefore the functionality can be essentiallylimitless.

An embodiment of the invention is illustrated in schematiccross-sectional view in FIG. 27. In FIG. 27 two electronic componentsare illustrated with the understanding that the two electroniccomponents could be a portion of a stack of electronic components. InFIG. 27 external terminations 32 ¹ and 32 ² are in electrical contactthrough a HTCA, 10, as described elsewhere herein. External terminations32 ³ and 32 ⁴ are not in electrical contact having instead a spacer, 9,there between wherein the spacer can be an air gap or a non-conductivematerial wherein the non-conductive material may be a HTIA. A secondaryadhesive, 12, which is preferably not conductive, adheres the body ofthe adjacent electronic components for stability purposes. The adhesivemay be in contact with one external termination of one electroniccomponent and the body of the adjacent electronic component. For thepurposes of the instant invention a secondary adhesive is an adhesivewhich is in mechanical contact with at least one body of at least oneelectronic component and may otherwise be in mechanical contact with abody of a second electronic component, an external termination of asecond electronic component or a solder pad.

An embodiment of the invention is illustrated in schematic side view inFIG. 28 wherein two stacks of electronic components, represented by 1-8without limit thereto, is illustrated mounted vertically to a substrate,36. A spacer, 17, is provided which functions as an insulator betweenadjacent external terminations of adjacent electronic components. Aswould be realized a stack as represented in FIG. 28 could be mountedhorizontally, as in FIG. 5, and alternate arrangements of HTCA, HTIA andspacers could be employed thereby allowing for combinations of serialand parallel electrical connections as set forth elsewhere herein.

An embodiment of the invention is illustrated in schematic side view inFIG. 29. In FIG. 29 a HTIA, 11, is between adjacent electroniccomponents thereby allowing for serial connectivity of the stackedelectronic component. Adjacent external terminations are in electricalconnection by HTCA's, 10, as described elsewhere herein. As would berealized a stack as represented in FIG. 29 could be mountedhorizontally, as in FIG. 5, and alternate arrangements of HTCA and HTIAcould be employed, with the further inclusion of spacers, therebyallowing for combinations of serial and parallel electrical connectionsas set forth elsewhere herein.

A particular advantage of the instant invention is an improvement ininductance. A high density multi-component stack mounting in ahorizontal direction, as in FIG. 5, reduces stray inductance as the pathlength between the electronic component and circuit board is reduced,and therefore so is the Equivalent Series Inductance (ESL). Furthermore,when mounted in the horizontal direction the Equivalent SeriesResistance (ESR) is also lowered since this results in shorterconnectivity pathways' to the components compared to the verticalmounting direction.

Each electronic component is preferably independently selected from thegroup consisting of capacitor, resistor, varistor, inductor, diode,fuse, overvoltage discharge device, sensor, switch, electrostaticdischarge suppressor, semiconductor and integrated circuit. The diodemay be a light emitting diode. More preferably the electronic elementsare selected from the group consisting of capacitor, resistor, varistor,inductor, diode, fuse, overvoltage discharge device, sensor, switch andelectrostatic discharge suppressor. It is preferred that the capacitoris an MLCC and more preferably at least one of the electronic componentsis an MLCC.

The external terminations of the electronic components are notparticularly limited herein with the proviso that they can be attachedto a pad, either active or mechanical by a HTCA or HTIA. TLPS is thepreferred HTCA interconnect between the external termination of theelectronic component and pad. The external termination may be onecomponent of TLPS, as will be more fully described herein, whereinadditional components of the TLPS are either inserted between theexternal termination to be bound or is integral to the surface to whichthe external termination is to be bound. The TLPS materials arecompatible with surface finishes containing silver, tin, gold, copper,platinum, palladium, nickel, or combinations thereof, either as leadframe finishes, component connections or inner electrodes to form anelectronically conductive metallurgical bond between two surfaces.

Transient liquid phase sintering (TLPS) adhesives form a termination toan electronic element or attach external terminations to a surface suchas a solder pad or adjacent external terminations thereby functioning asan interconnect. TLPS terminations have the advantage of being able toaccommodate different surface finishes as well as electronic elements ofdiffering lengths. Furthermore, since no solder balls are formedelectronic elements can be stacked on top of each other with only TLPSthere between and without the gaps normally required for cleaning aswith solder attachment technology. TLPS can be directly bonded with theinner electrodes of the electronic component, when the electronicelement is an MLCC, and the termination can be formed at lowtemperature. In an embodiment, higher density terminations can beprepared by using a thermo-compression process thereby forming improvedexternal lead attachment bonds.

Solders are alloys which do not undergo a change in composition afterthe first reflow. Solders have only one melting point and can bere-melted an indefinite number of times. A common solder is 60% Sn40%Pb. Solders have been the materials of choice in electronics to providethe mechanical and electrical interconnects between electronic elementsand circuit boards or substrates. Solders are very well suited for massvolume production assembly processes. The physical properties of soldercan be altered simply by changing the ratios or the metals used tocreate a solder alloy. When solder is referenced herein it will imply analloy of at least two metals that can be re-melted multiple times atnearly the same temperature.

Transient liquid phase sintering (TLPS) bonds are distinguishable fromsolders. TLPS materials are mixtures of two or more metals or metalalloys prior to exposure to elevated temperatures thereby distinguishingthe thermal history of the material. TLPS materials exhibit a lowmelting point prior to exposure to elevated temperatures, and a highermelting point following exposure to these temperatures. The initialmelting point is the result of the low temperature metal or an alloy oftwo low temperature metals. The second melting temperature is that ofthe intermetallic formed when the low temperature metal or alloy forms anew alloy with a high temperature melting point metal thereby creatingan intermetallic having a higher melting point. This is particularlyadvantageous when used as the HTCA in the high-density package since theTLPS melting point can be easily selected to be higher than that of theinterconnects used in the circuit board assembly. TLPS materials form ametallurgical bond between the metal surfaces to be joined. Unliketin/lead or lead (Pb) free solders, the TLPS adhesives do not spread asthey form the intermetallic joint. Rework of the TLPS system is verydifficult due to the high secondary reflow temperatures. TransientLiquid Phase Sintering is the terminology given to a process to describethe resulting metallurgical condition when two or more TLPS compatiblematerials are brought in contact with one another and raised to atemperature sufficient to melt the lower temperature metal. To create aTLPS process or interconnect at least one of those metals is from afamily of metals having a low melting point, such as tin (Sn) or indium(In), and the second metal is from a family having high melting points,such as copper (Cu) or silver (Ag). When Sn and Cu are brought together,and the temperature elevated, the Sn and Cu form CuSn intermetallics andthe resulting melting point is higher than the melting point of themetal having a low melting point. In the case of In and Ag, whensufficient heat is applied to the In to cause it to melt it actuallydiffuses into the Ag creating a solid solution which in turn has ahigher melting point than the In itself. TLPS will be used togenerically reference the process and the TLPS compatible materials usedto create a metallurgical bond between two or more TLPS compatiblemetals. TLPS provides an electrical and mechanical interconnect that canbe formed at a relatively low temperature (<300° C.) and having asecondary re-melt temperature >600° C. These temperatures are determinedby the different combination of TLPS compatible metals. TLPS will beused to generically pertain to the process and materials used to createa TLPS metallurgical bond or interconnect. The rate of diffusion orsintering is a time temperature function and is different for thedifferent combinations of metals. The result is a solid solution havinga new melt temperature approaching that of the high temperature meltingmetal.

The TLPS technology is particularly suited to providing both amechanical and electrical conductive metallurgical bond between twomating surfaces preferably that are relatively flat. The metalstypically used for the TLPS process are selected from two metalfamilies. One consists of low melting temperature metals such as indium,tin, lead, antimony, bismuth, cadmium, zinc, gallium, tellurium,mercury, thallium, selenium, or polonium and a second family consistingof high temperature melting metals such as silver, copper, aluminum,gold, platinum, palladium, beryllium, rhodium, nickel, cobalt, iron andmolybdenum to create a diffused solid solution.

It is highly desirable to use a flux free process to eliminate anypotential voids within the joint. Since TLPS is a sintering basedprocess, the bond line is uniform and void free. Fluxes, which arenecessary with solders, get entrapped in the joint and are subsequentlyburned out leaving a void. In the case with the semi-conductor industry,and specifically with die attach processes, these voids can create hotspots within the integrated circuit (I/C) which can lead to prematurefailure and reliability issues. TLPS addresses this issue since TLPS isa sintering process and free of fluxes. When the two metals are matedtogether and heat is applied, the lower melting metal diffuses into thehigher melting metal to create a solid solution across the matingsurface area. To create a solid uniform bond line it is mandatory thatthe mating surfaces be flat and coplanar to insure intimate contactacross the entire mating surface. The required flatness of the matingsurfaces also limits the application of this technology because thereare many surfaces that are not sufficiently planar to yield a goodjoint.

The use of TLPS in paste form allows uneven surfaces to be joined. Morespecifically, the use of TLPS in paste form allows two irregular shapedsurfaces to be joined with no intimate, or continuous, line of contact.A TLPS compatible metal particle core combined with a liquid carriermaterial to form a paste can be applied between two non-planarnon-uniform surfaces having mixed surface preparation technologies suchas plating, sintered thick film, and or plated sintered thick film andthen heating to the melting temperature of the metal having the lowestmelting point and holding that temperature for a sufficient amount oftime to form a joint. A single metal particle core eliminates the needfor multiple metals in a paste thus making the ratios of metals anon-issue. It is also possible to create a single particle by usingsilver, a metal having a high melting point of approximately 960° C. asa core particle, and then coating that particle with a metal shellhaving a low temperature metal such as indium having a melting point of157° C.

A two-step reflow can also be used with the transient liquid phasesintering process wherein in the first step an electrically conductivemetallurgical bond is formed at low temperature using a relatively shorttime cycle, in the range of 5 seconds to 5 minutes, and low temperature,in the range of 180° C. to 280° C., depending on the metals being usedin the TLPS alloying process. In the second step the part is subjectedto an isothermal aging process using a temperature range of 200° C. to300° C. for a longer duration such as, but not limited to, 5 minutes to60 minutes. The shorter times required to form the initial bond are wellsuited for an automated process. In another method a single step processcan be used wherein the TLPS forms a terminal, or conductivemetallurgical bond, between the external leads and electronic element(s)at temperatures of, for example, 250° C. to 325° C. for a duration of,for example, 10 seconds to 30 seconds. Lower temperatures, such as 175°C. to 210° C., can be used for a longer duration, such as 10 to 30minutes. This is particularly useful when the electronic componentitself is sensitive to temperature.

Indium powder mixed with a flux and solvent to form a paste can beapplied to produce a TLPS metallurgical bond between two coupons havinga base metal of copper overplated with Ni and then overplated with about5 microns (200 μinches) of silver. The samples can be prepared bydispensing the indium paste onto a coupon having the plated surfaces asmentioned and then placing two coupons in contact with one another andheating to 150° C. for 5 seconds, followed by increasing the temperatureto about 320° C. for about 60 seconds. The joint strength of the samplethus prepared can exhibit a pull weight in the range of 85-94 poundsequating to shear stress of 4,177 psi and a pull peel weight in therange of 5-9 pounds with an average of 7 pounds can be achieved. Theseresults are comparable to results for SnPb solders having shearstrengths of approximately 3000 psi and pull peel strengths in the 7-10pound range. One major difference is that the Agln joint can withstandsecondary melt temperatures exceeding 600° C. These results indicatethat the In paste used to bond two silver plated coupons is at leastequivalent if not stronger than current solder SnPb solders but also hasa much higher secondary melt temperature thus yielding a materialsuitable for high temperature interconnect applications and also beinglead free. The TLPS paste or preform may have inert fillers therein toserve two purposes. One purpose is to minimize the cost due to expensivemetals and the second purpose is to make direct electrical andmetallurgical bonds directly to the non-terminated ends of theelectronic element and exposed internal electrodes. The cost can bereduced, particularly, when a gap is to be filled by replacing a portionof, particularly, the high melting metal component with an inertmaterial or with a lower cost conductive material. Particularlypreferred fillers for use in place of the high melting point metal arenon-metals such as ceramics with melting points >300° C. and glasses orhigh temperature polymers with glass transition temperatures(T_(g))>200° C. An example would be thermosetting polymers such aspolyimide. Two particular advantages of replacing the high melting pointmetal with one of these non-metals is that the active low melting pointmetal of the TLPS will not be consumed by diffusion during the TLPS bondformation. The second advantage of inert fillers when selected from afamily of glasses having low melting points is that the glass within themixture of the TLPS paste or preform will create a bond with the exposedglass frit of the non-terminated and exposed ceramic body of, forexample, an MLCC. The non-metals can also be coated with the low meltingpoint metal by methods such a spraying or plating.

Sintered metal interconnects of silver as well as nano-silver andnano-copper can also be used to form HTCA interconnects. The resultinginterconnect can be formed using a low temperature sintering process butthe bond formed has the high melting point of the associated with themetal, in the case of silver 960° C. However, these processes oftenrequire elevated pressures for prolonged times in batch operation thatcan limit throughput compared CuSn TLPS. Also, nano-sized metals can beprohibitively expensive.

Diffusion soldering can also be used as a joining method to form theHTCA interconnect. This combines features of conventional soldering anddiffusion bonding processes. The process relies on reaction between athin layer of molten solder and metal on the components to form one ormore intermetallic phases that are solid at the joining temperature.Since a low melting point material, solder reacts with a higher meltingpoint metal this may also be considered in the broader definition ofTLPS.

Direct copper bonding can also be used as the HTCA but this is a hightemperature diffusion process primarily used in die attach so could bedetrimental to some components.

Methods to adhere an external termination to a solder pad or adjacentexternal termination can comprise coating two mating surfaces one with ahigh melting point metal and its mating surface with a low melting pointmetal. The coating process may consist of vapor deposition or plating. Asecond method is to sandwich a preform film made from a low meltingpoint metal or an alloy of two or more low melting point metals betweentwo planar surfaces coated with a high melting point metal. A thirdmethod is to create a paste consisting of particles of a high meltingpoint metal such as copper and then adding particles of two alloyed lowmelting point metals and mixed into a dual purpose liquid that cleansthe surfaces to be bonded and also serves as the liquid ingredient tothe metal particles to form a paste mixture.

If full diffusion of the two metals is not complete in the stated cycletime and the maximum secondary reflow temperature is not reached, thejoint can be subjected to a second heating process. In this case thejoint, or assembly, can be subjected to a temperature higher than thatof the low melting point material and held for a period of time from 15minutes up to 2 hours. The time and temperature can be varied to providea desirable secondary reflow temperature as dictated by secondaryassembly processes or final environmental application requirements. Inthe case of the indium/silver TLPS, secondary melt temperatures inexcess of 600° C. can be achieved.

In addition to applying a paste to form a TLPS alloy joint betweensuitable surfaces this can also be achieved with a preform. In itssimplest manifestation the preform can be a thin foil of the lowtemperature TLPS component. Alternatively, the preform can be producedby casting and drying the paste to remove the solvent. The resultingsolid preform can be placed between the surfaces to be bonded. In thiscase it may be necessary to add a suitable binder to the paste foradditional strength after drying. In all these cases the preform shouldbe malleable such that it can conform to the surfaces to be bonded.

An HTCA can be an interconnect comprising a single metal, such asindium, contained within a paste which can be used to form a bond to asurface coated with a high melting point metal, such as silver. Thediffusion of the indium into silver allows a lower temperature transientliquid phase to form that subsequently reacts to achieve a highertemperature bond. Achieving a high rate of diffusion in the lowermelting point paste is critical to this bond formation. In order toachieve the desired properties in the final joint, such as reduced voidsand a homogeneous phase the addition of other metals to the paste may bedesirable. However, it is critical to retain the high diffusivity of thelow melting point material. For this reason if one or more metals arerequired in addition to the low melting point metal it is preferred thatthese be incorporated by coating the metal powders prior to forming thepaste. Coating the lowest melting point metal onto the higher meltingpoint metal is preferred to retain an active surface. Coatings also havethe desired effect of reducing the diffusion lengths between thedifferent metallic elements of the paste allowing preferred phases to bemore readily formed as opposed to a simple mixing of one or moreadditional metal powders to the single metal paste.

Conductive adhesives as HTCA's are typically cross linking polymersfilled with silver or gold particles that cure or cross link within aspecified temperature range, generally 150° C., to form a mechanicalbond to the materials to be joined. Their conductivity is created by themetal particles making intimate contact with one another, within theconfines of the polymer matrix, to form an electrically conductive pathfrom one particle to another. Because the binder is organic in nature,they have relatively low temperature capabilities, normally in the rangeof about 150° C. to about 300° C. Conductive epoxies, once cured, cannotbe reworked. Unlike TLPS bonds, exposure to high heat or corrosiveenvironments may decompose the polymeric bonds and oxidize the metalparticles degrading the electrical properties. Both the electrical andmechanical performance of the interconnect can be compromised resultingin increased ESR and decreased mechanical strength.

Polymer solders HTCA's may comprise conventional solder systems based onPb/Sn alloy systems or lead free systems, such as Sn/Sb, which arecombined with crosslinking polymers which serve as cleaning agents. Thecross-linked polymers also have the ability to form a cross-linkedpolymer bond, such as an epoxy bond, that forms during the melting phaseof the metals thereby forming a solder alloy and a mechanical polymericbond. An advantage of polymer solders is that the polymeric bondprovides additional mechanical bond strength at temperatures above themelting point of the solder, thus giving the solder joint a higheroperating temperature in the range of about 5 to 80° C. above themelting point of the solder. Polymer solders combine current solderalloys with a cross linking polymer within the same paste to provideboth a metallurgical bond and a mechanical bond when cured, such as byheating, to provide additional solder joint strength at elevatedtemperatures. However, the upper temperature limits and joint strengthhas been increased, just by the physical properties of the materials. Apractical limit of 300° C. remains whereas the bonds created by TLPS canachieve higher temperatures.

In many applications a high degree of porosity may be acceptable.However, in harsh environments, such a high humidity or in circuit boardmounting processes, high porosity is not desirable since water or otherchemicals may penetrate through the bond which may cause the bond tofail. A preferred embodiment of this invention is therefore to form alow porosity termination within the transient liquid phase sinteringjoint using a thermo-compression bonding process. This process has theadded advantage of using a low process time of 15 to 30 seconds at atemperature in the range of 225° C. to 300° C. in a single step makingit suitable for automation. Robust joints can be created for theapplication of attaching external leads to electronic elements, whenleads are used, with a one-step low temperature process in less than 30seconds and in combination with thermo-compression bonding.

Thermo compression bonding is also a preferred processing method whenusing polymer solder because it assists in the formation of ahigh-density metallurgical bond between the contacting surfaces. Theadvantages of thermo-compression include a more robust bond with respectto secondary attachment processes and attachments with higher strengthare achieved. A compressive force of 0.5 to 4.5 Kilograms/cm² (7.1 to 64psi) and more preferably 0.6 to 0.8 Kilograms/cm 2 (8.5 to 11 psi) issufficient for demonstration of the thermo-compression teachings herein.About 0.63 Kilograms/cm2 (9 psi) is a particularly suitable pressure fordemonstration of the teachings.

It is highly desirable to create a joint with minimum porosity thatexhibits the following characteristics: strong mechanical strength inexcess of 5 Lbs./inch for Pull Peel test, Tensile, and Shear highelectrical conductivity, low initial process temperature in the range of150° C. to 225° C., a secondary reflow temperature in excess of 300° C.or higher, between non-uniform surfaces making intimate contact orhaving gaps up to 0.015 inches.

High temperature insulating adhesives can be a thermal or moisture setadhesives, UV cure adhesives or pressure sensitive adhesives.Particularly preferred high temperature insulating adhesives includeepoxy resins, phenolic formaldehyde resins, phenolic melamineformaldehyde resins, phenolic neoprene, resorcinol formaldehydes,polyesters, polyimides, cyanoacrylates, acrylics, styrene blockcopolymers, styrene butadiene copolymers, polyurethanes, polyarylenes,polysulfides, polyamides, silicones and waxes etc. The HTIA may beselected to form a bond at the same time as the HTCA or in somecircumstances, it may be preferable to provide a separate bondingprocess. The HTIA bonding processes may be achieved by heating, UVcuring, moisture curing or hot melt deposition. Additionally, the HTIAmay contain inert fillers of sufficient size and dielectric propertiesto ensure minimal dielectric spacing between adjacent components asrequired by the circuit/stack design and service conditions.

The material of construction for the substrate is not particularlylimited herein with standard printed circuit board (PCB) materials beingsuitable for use. Laminates, fiber reinforced resins, ceramic filledresins, specialty materials and flexible substrates are particularlysuitable. Flame Retardant (FR) laminates are particularly suitable as aninterposer material and especially FR-1, FR-2, FR-3, FR-4, FR-5 or FR-6.FR-2 is a phenolic paper, phenolic cotton paper or paper impregnatedwith phenol formaldehyde resin. FR-4 is particularly preferred which isa woven fiberglass cloth impregnated with epoxy resin. Composite epoxymaterials (CEM) are suitable and particularly CEM-1, CEM-2, CEM-3, CEM-4or CEM-5 each of which comprise reinforcement such as a cotton paper,non-woven glass or woven glass in epoxy. Glass substrates (G) are widelyused such as G-5, G-7, G-9, G-10, G-11 and others with G-10 and G-11being most preferred each of which is a woven glass in epoxy.Polytetrafluoroethylene (PTFE), which can be ceramic filled, orfiberglass reinforced such as in RF-35, is a particularly suitablesubstrate. Electronic grade ceramic materials such as polyether etherketone (PEEK), alumina or yttria stabilized zirconia are available with96% Al₂O₃ and 99.6% Al₂O₃ being readily available commercially.Bismaleimide-Triazine (BT) epoxy is a particularly suitable substratematerial. Flexible substrates are typically a polyimide such as apolyimide foil available commercially as Kapton or UPILEX or apolyimide-fluoropolymer composite commercially available as Pyrelux.Ferrous alloys are also used such as Alloy 42, Invar, Kovar ornon-ferrous materials such as Cu, Phosphor Bronze or BeCu.

The package, or portions of the package, can be over-molded by anon-conductive polymer or resin. The material used for over-molding isnot particularly limited herein. Over-molding can be done to isolate thepackage, or components therein, from electrical interaction with otherelements of a circuit or to protect the package, or components therein,from environmental variations. Over-molding can also be beneficial forlabeling and for use with pick-and-place equipment since theover-molding can be applied with specific geometry identifiable byoptical or mechanical equipment. Additionally, the package can bemechanically encapsulated in a case, shell or other assembly for use asa plug in electrical circuit or assembly utilizing commerciallyavailable electrical connections attached to the package via extantassembly methodologies.

The invention has been described with reference to the preferredembodiments without limit thereto. Additional embodiments andimprovements may be realized which are not specifically set forth hereinbut which are within the scope of the invention as more specifically setforth in the claims appended hereto.

The invention claimed is:
 1. A method for forming a high densitymulti-component package comprising: providing at least two electroniccomponents wherein each electronic component of said electroniccomponents comprises a first external termination and a second externaltermination; forming a stack of adjacent said electronic components;attaching adjacent said first external terminations with a firstadhesive there between; attaching adjacent said second externalterminations with a second adhesive there between wherein said secondadhesive is a high temperature insulating adhesive; and wherein saidadjacent electronic components are connected serially.
 2. The method offorming a high density multi-component package of claim 1 wherein saidfirst adhesive is a high temperature conductive adhesive and said hightemperature insulating adhesive are bonded to the components in the sameprocess.
 3. The method of forming a high density multi-component packageof claim 1 wherein said first adhesive is a high temperature conductiveadhesive and a said high temperature insulating adhesive are bonded tothe components in separate processes.
 4. The method for forming a highdensity multi-component package of claim 1 further comprising a spacerbetween adjacent second external terminations.
 5. The method for forminga high density multi-component package of claim 4 wherein said spacer isselected from an air gap and a non-conducting material.
 6. The methodfor forming a high density multi-component package of claim 1 furthercomprising a secondary adhesive.
 7. The method for forming a highdensity multi-component package of claim 1 wherein each said electroniccomponent is independently selected from the group consisting ofcapacitor, resistor, varistor, inductor, diode, fuse, overvoltagedischarge device, sensor, switch, electrostatic discharge suppressor,semiconductor and integrated circuit.
 8. The method for forming a highdensity multi-component package of claim 7 wherein said capacitor anMLCC.
 9. The method for forming a high density multi-component packageof claim 8 wherein said electronic component is selected from the groupconsisting of MLCC, resistor, varistor, inductor, diode, fuse,overvoltage discharge device, sensor, switch and electrostatic dischargesuppressor.
 10. The method for forming a high density multi-componentpackage of claim 9 wherein at least one said electronic component is anMLCC.
 11. The method for forming a high density multi-component packageof claim 9 wherein said diode is a light emitting diode.
 12. The methodfor forming a high density multi-component package of claim 1 whereinall electronic components are serially connected.
 13. The method forforming a high density multi-component package of claim 1 wherein atleast two additional electronic components are electrically connected inparallel.
 14. The method for forming a high density multi-componentpackage of claim 1 comprising at least two stacks wherein a secondaryelectrical component spans said stacks.
 15. The method for forming ahigh density multi-component package of claim 14 wherein said secondaryelectrical component is selected from the group consisting ofinterposer, capacitor, resistor, varistor, inductor, diode, fuse,overvoltage discharge device, sensor, switch, electrostatic dischargesuppressor, semiconductor and integrated circuit.
 16. The method forforming a high density multi-component package of claim 14 wherein saidsecondary electrical component is in electrical parallel with at leasttwo said electronic components.
 17. The method of forming a high densitymulti-component package of claim 1 further comprising a high temperatureconductive adhesive is selected from the group consisting of solder,conductive adhesive, polymer solder and transient liquid phase sinteringadhesive.
 18. The method for forming a high density multi-componentpackage of claim 17 wherein said liquid phase sintering adhesivecomprises a high melting point metal and a low melting point metal. 19.The method for forming a high density multi-component package of claim18 wherein said low melting point metal is selected from the groupconsisting of indium, tin, lead, antimony, bismuth, cadmium, zinc,gallium, tellurium, mercury, thallium, selenium, or polonium.
 20. Themethod for forming a high density multi-component package of claim 18wherein said high melting point metal is selected from the groupconsisting of silver, copper, aluminum, gold, platinum, palladium,beryllium, rhodium, nickel, cobalt, iron and molybdenum.
 21. The methodfor forming a high density multi-component package of claim 18 whereinsaid transient liquid phase sintering adhesive comprises tin and copperor indium and silver.
 22. The method for forming a high densitymulti-component package of claim 1 wherein at least one said externaltermination comprises a metal selected from the group consisting ofsilver, tin, gold, copper, platinum, palladium and nickel.
 23. Themethod of forming a high density multi-component package of claim 1wherein said high temperature insulating adhesive is selected from epoxyresins, phenolic formaldehyde resins, phenolic melamine formaldehyderesins, phenolic neoprene, resorcinol formaldehydes, polyesters,polyimides, cyanoacrylates, acrylics, styrene block copolymers, styrenebutadiene copolymers, polyarylenes, polyurethanes, polysulfides,polyamides, silicones and waxes.
 24. The method for forming a highdensity multi-component package of claim 1 wherein said high densitymulti-component package is selected from the group consisting of a Pifilter, a T filter and an LC filter.
 25. The method for forming a highdensity multi-component package of claim 1 further comprising asubstrate.
 26. The method for forming a high density multi-componentpackage of claim 25 wherein said substrate comprises at least twocircuit traces.
 27. The method for forming a high densitymulti-component package of claim 26 wherein said substrate comprises atleast three circuit traces.
 28. The method for forming a high densitymulti-component package of claim 1 further comprising a flexiblecircuit.
 29. The method for forming a high density multi-componentpackage of claim 1 further comprising overmolding.
 30. A method forforming a high density multi-component package comprising: providing atleast three electronic components wherein each electronic component ofsaid electronic components comprises a first external termination and asecond external termination; forming a stack of adjacent said electroniccomponents; attaching a pair of adjacent said first externalterminations with a first adhesive there between wherein said firstadhesive is a high temperature conductive adhesive; attaching a pair ofadjacent said second external terminations with a second adhesive therebetween wherein said second adhesive is a high temperature insulatingadhesive; and wherein said adjacent electronic components are connectedserially.